Possibly a dangerous site?

While my friends were over, they went onto my computer and went on this site called "Omegle.com". This site is like chatroulette, where you announymously talked to strangers through chat. Now, my friends being the idiots they are, entered some weird tags, and started saying weird stuff to mess with some people. I became worried because they were on my computer and I didn't want anything bad to happen. I googled to try and figure out if this site was dangerous. Some people said that other could hack others, and others said there was no possible way. Could someone verify? My mac's FireWall was on, and im on a WAP2 wireless router connection, all sharing is turned off, and i've downloaded Kaspersky Virus Scaner, and iAntivirus from the mac appstore. I've ran the virus scan on iAntivirus and it came up with zero viruses. Then I ran a quick scan, and then a full scan on Kaspersky Virus Scanner. Both scans found zero threats detected. Is there anyway to check my computer if someone did hack it? or to restore my computer that could eliminate any possible danger if there is one? Thanks in advance!